Seismic Risk for the Largest Cities of the World; Intensity VIII or More

Abstract

General methodology of probabilistic estimation of seismic risk, as a base for decision making, is described by an analysis of seismic risk for the cities with population ≥ 1 mln in active seismic regions of the world. The estimations are based on seismotectonic regionalization of the world and on the three models: of earthquake occurrence, strong motion (isoseists) and dynamics of population. The estimations are tested by comparison with actual earthquake history of the cities considered. The test is successful, in spite of the fact, that all these models are grossly averaged due to the usual incompleteness of the data. This shows, that available data may be sufficient to estimate the seismic risk for a large set of objects, while not for each separate object. During the 30 years, 1971-2000, 8 ± 3.5 cities and 40.1 ± 21.6 mlns of people in these cities will experience strong motions with macroseismic intensity ≥ VIII MM (Modified Mercalli Scale). Counted are only the events, when such shaking covers ≥ 100 km2, so that each event does spell disaster. The second estimation is large due to the explosion of urban population. More conservative data on the population growth reduce this estimation not more, than by 30 %. It indicates, that global seismic risk is rapidly increasing, presenting new unexplored problems.